SPARTANBURG, S.C. — Republican presidential contenders blasted President Barack Obama’s policies on Iran and Afghanistan Saturday night as badly misguided and weak — and unlikely to lead to lasting peace in either nation.

Iran “of course is President Obama’s greatest failing from a foreign policy standpoint,” said former Massachusetts Gov. Mitt Romney. Former House Speaker Newt Gingrich charged that Obama “skipped all the ways to be smart” with his Iran strategy.

Texas Gov. Rick Perry said Obama had engaged in “irresponsible leadership” in Afghanistan.

The candidates clashed at the “commander-in-chief debate” at Wofford College here, the first debate of the campaign to focus solely on national security and foreign policy. It was held in a state that will hold the first Southern primary, on Jan. 21.

The debate was the first since Gingrich vaulted into the top tier of GOP candidates. A McClatchy-Marist nationwide poll, conducted Nov. 8 to 10, showed that while Romney led among Republicans and GOP-leaning independents with 23 percent, Gingrich was now second at 19 percent. Businessman Herman Cain, whose momentum has stalled since allegations surfaced that he had sexually harassed several women in the past, slipped to third at 17 percent.

Of the eight Republican candidates, only Jon Huntsman, Obama’s ambassador to China from 2009 until early this year and ambassador to Singapore in the George H. W. Bush administration, has extensive foreign policy experience.

The candidates offered different approaches to dealing with Iran. Tuesday, the International Atomic Energy Agency, the United Nations’ nuclear watchdog, said Iran was apparently trying to make a nuclear weapon, adding that covert efforts may be ongoing. Friday, the agency produced correspondence, diagrams and satellite images to bolster its claim.

Iran called the report “a mere lie,” but Secretary of State Hillary Rodham Clinton has said the United States is still waiting for Iran’s official response.

Cain urged more help be given to Iranian dissidents to promote “regime change,” but stopped short of urging military action. Romney, though, said it should be an option “if all else fails.”

“The President should have built a credible threat of military action and made it very clear the United States of America is willing in the final analysis to take military action to keep Iran from developing a nuclear weapon,” Romney said.

“If we elect Barack Obama, Iran will have a nuclear weapon,” he added. “If you elect me as President, Iran will not have a nuclear weapon.”

Gingrich said the United States should be working now with Israel on maximum covert operations against Iran, including “taking out” its nuclear scientists, to take “whatever steps are necessary” to prevent it from gaining nuclear weapons.

The candidates were particularly critical of Obama’s Afghanistan policy. Obama plans to withdraw by next September the troops he sent last year as part of a surge in forces there and to hand over security responsibilities to the Afghan government by 2014.

Romney blasted Obama for bringing home troops early — with an eye on the 2012 election. Perry and Minnesota Rep. Michele Bachmann made similar points.

Gingrich had a broader view. “We don’t have a clue how hard this is going to be,” said Gingrich. “This has to be a much larger strategic discussion’’ that includes how to handle Afghan neighbors Iran and Pakistan.

Huntsman differed. “I say it’s time to come home,” he said, since the United States has achieved its objectives and has bigger priorities elsewhere. “This nation’s future is not Afghanistan.”

Also participating in the debate were Texas Rep. Ron Paul and former Sen. Rick Santorum of Pennsylvania.